The present invention relates to a method of removing a film containing an organic composition and, more particularly, to a method of removing a photoresist film containing an organic polymer compound used in a photolithographic process for producing a semiconductor device and the like, and to an apparatus used in the method.
A photoresist material is generally used in a photolithographic process for forming a fine pattern and/or in a subsequent etching step for forming an electrode pattern in course of manufacturing a semiconductor device, such as an integrated circuit, a transistor, a liquid crystal device, a diode and the like.
For example, when a silicon oxide layer is formed in a desired pattern on a semiconductor substrate such as a silicon substrate (referred to as a silicon wafer), a silicon oxide layer is first deposited on the surface of the substrate and cleaned before a photoresist material suited for forming the desired pattern is applied to the silicon oxide layer to form a photoresist film. Then, a photo mask having a pattern corresponding to the desired pattern is placed on the photoresist film, exposed to light and then developed. Thereby, a photoresist film having the desired pattern, referred to a photoresist pattern, is obtained. In the subsequent etching step, the silicon oxide layer is removed according to the resulting photoresist pattern. Finally, after the removal of the remaining photoresist film and the cleaning of the surface of the substrate, the silicon oxide layer is remained on the substrate in the desired pattern.
In the etching step, an art-known method of removing a part of the photoresist film unnecessary for the formation of the desired pattern includes, for example, [1] a method using an oxygen gas plasma and [2] a method using various oxidizing agents.
In the method using an oxygen gas plasma [1], oxygen gas is introduced in the photoresist film under vacuum and a high voltage generates an oxygen gas plasma. Then, the photoresist film is decomposed and removed by reacting with the oxygen gas plasma. However, there had been some problems in this method [1], including the requirement of an expensive apparatus for generating the oxygen gas plasma, a potential of damaging the substrate containing an electrical element due to the presence of charge carriers in the plasma, and the like.
Alternatively, as an example of the method [2] using various oxidizing agents to decompose and remove the photoresist film, for example, a method using hot concentrated sulfuric acid or a mixture of hot concentrated sulfuric acid and hydrogen peroxide as the oxidizing agent is known.
When using hot concentrated sulfuric acid, however, there is a disadvantage, such as an extremely high risk of heating strong sulfuric acid to 150xc2x0 C.
On the other hand, when using the mixture of hot concentrated sulfuric acid and hydrogen peroxide, a substance having an oxidizing and decomposing action is released according to the following scheme. In the scheme, on adding hydrogen peroxide to hot concentrated sulfuric acid heated to about 140xc2x0C., peroxosulfuric acid (H2SO5; generally referred to as Caro""s acid) and oxygen atom (O) are generated as follows:
H2SO4+H2O2⇄H2SO5+H2Oxe2x80x83xe2x80x83(1) 
H2O2xe2x86x92O+H2Oxe2x80x83xe2x80x83(2) 
The organic photoresist film may be oxidized by the strong acidity of both peroxosulfuric acid and oxygen atoms and converted to an inorganic substance. The inorganic substance is decomposed by reacting with hot concentrated sulfuric acid and then removed from the surface of the substrate.
However, as shown in the above schemes (1) and (2), this method [2] has a problem that, since a sulfuric medium is diluted with water produced upon addition of hydrogen peroxide to hot concentrated sulfuric acid, the concentration of hot concentrated sulfuric acid after mixing is decreased with time. The method [2] also has disadvantages, including the extremely high risk as described for the method [1], i.e., the use of strong sulfuric acid at an elevated temperature, and the heat generated when mixing hot concentrated sulfuric acid with hydrogen peroxide, and the necessity of an expensive exhaust system generating strong ventilation in order to operate the method in a clean room, and the like.
As another oxidizing agent used to decompose the photoresist film other than hot concentrated sulfuric acid, there has been developed a water-immiscible solution for exclusively removing a photoresist film, such as, for example, a solution #106 consisting of 30% by volume of dimethylsulfoxide and 70% by volume of monoethanolamine. However, such oxidizing agent has problems, including its lower oxidation power than hot concentrated sulfuric acid and a mixture of hot concentrated sulfuric acid and hydrogen peroxide, and the difficulty of treating the foul solution which is immiscible with water.
In order to overcome the problems of the above methods [1] and [2], a method of removing a photoresist film using a mixture of ozone with hot sulfuric acid as the oxidizing agent has been proposed (Japanese Patent Kokai Publication No. Sho 57-180132). This publication discloses a method to decompose and remove the organic substance (i.e. the photoresist film) or the inorganic substance deposited on the substrate or the insulating layer by bubbling an ozone-containing gas in hot sulfuric acid. It also describes a washing apparatus used in the method (the cross sectional view of the apparatus is illustrated in FIG. 8).
The washing apparatus shown in FIG. 8 includes a quartz container 6xe2x80x3 filled with hot concentrated sulfuric acid 5xe2x80x2 heated at approximately 110 xc2x0 C., which is laid on a heater 11 and a quartz tube 120 having plural outlets 3xe2x80x2. A raw gas (generally, oxygen) supplied through a gas-introducing tube 111 provided outside the quartz container 6xe2x80x3 is converted to an ozonized gas in an ozone generator 1. The ozonized gas is then injected through the quartz tube 120 into hot concentrated sulfuric acid 5xe2x80x2 in the quartz container 6 to react with sulfuric acid, and thereby, peroxosulfuric acid and an oxygen atom are produced. By oxidizing the photoresist film with the strong acidity of both peroxosulfuric acid and oxygen, the photoresist film on the surface of the substrate 8 (held with a substrate cassette 9), which is immersed in hot concentrated sulfuric acid, is removed.
In the method described in this publication, the concentration of the sulfuric acid does not change since water is not generated during the decomposition of the photoresist film, and, therefore, frequency of changing the sulfuric acid may be decreased. The method, however, had a problem that the cost for raw materials is too high because a large amount of the sulfuric acid is needed to operate. Additionally, the method and apparatus disclosed in the publication also have a high risk on working because of the use of strong sulfuric acid at an increased temperature in the same way as the conventional method, and also needs extremely strong ventilation since the oxidizing agent is vaporized by bubbling of the ozonized gas.
Accordingly, an object of the present invention is to provide a method of removing a photoresist film at an increased rate, which decreases both usage of the raw materials and the cost for the exhaust system and is also environment-friendly, and to further provide an apparatus used in the method, in order to overcome the above problems with the art-known method for removing the photoresist film and with the conventional apparatus used therefor.
Definition of the Technical Terms
As used herein, an xe2x80x9cozonized gasxe2x80x9d means a gas mixture containing oxygen and a given amount of ozone. Hereinafter, a xe2x80x9csealed systemxe2x80x9d is thermodynamically classified into an open system, but it means one in which any of a gas and a solution are introduced therein and a gas or a vapour generated in removing a photoresist film according to the present invention, and the like, are not released or spattered outside of the system.
According to the first aspect of the present invention, there is provided a method of removing a photoresist film provided on a surface of a substrate, comprising steps of in a sealed system, disposing the substrate surface having the photoresist film to contact with a photoresist film removing solution, making ozone exist in gas phase and/or solution phase in the vicinity of the liquid surface of the photoresist film removing solution, and changing a relative position between the surface of the substrate and the liquid surface of the solution to decompose or remove the photoresist film from the substarate, characterized in that the relative position is changed continuously or intermittently within a range between a position where a bottom edge of the substrate is present above the liquid surface of the solution, and another position where a top edge of the substrate is present below the liquid surface of the solution.
The photoresist film removing solution used in the present invention may be a solution which is able to dissolve a desired quantity of ozone, and may be selected from a group consisting of pure water, an acid and alkaline aqueous solutions and an organic solvent. According to the method of the present invention, ozone and the photoresist film removing solution may be simultaneously or separately supplied into a sealed system. Alternatively, ozone and the photoresist film removing solution may also be supplied simultaneously by incorporating ozone into the photoresist film removing solution.
In the method of the present invention, the relative position between the surface of the substrate and the liquid surface of the photoresist film removing solution can be controlled by the way of:
(1) moving the substrate itself; or
(2) changing a level of the liquid surface of the photoresist film removing solution.
The moving and changing may be continuously or intermittently conducted.
According to the method of the present invention, the photoresist film removing solution may be used in a mixed phase prepared by incorporating a given amount of ozone therein. It may be also possible to apply ultrasonic vibration into the sealed system.
Another method of the present invention includes a step of continuously or intermittently supplying the surface of the substrate having the photoresist film thereon with an ozonized gas and the photoresist film removing solution in a form of mist. In this method, ozone and the photoresist film removing solution may be simultaneously supplied by using the photoresist film removing solution which incorporates ozone therein.
According to the method of the present invention, the photoresist film removing solution which has been used in the system may be recovered and conditioned for reuse.
According to the second aspect of the present invention, there is provided an apparatus for removing a photoresist film from a substrate used in a method of removing the photoresist film provided on a surface of the substrate, comprising steps of in a sealed system, disposing the substrate surface having the photoresist film to contact with a photoresist film removing solution, making ozone exist in gas phase and/or solution phase in the vicinity of the liquid surface of the photoresist film removing solution, and changing a relative position between the surface of the substrate and the liquid surface of the solution to decompose or remove the photoresist film from the substarate, the relative position is changed continuously or intermittently within a range between a position where a bottom edge of the substrate is present above the liquid surface of the solution, and another position where a top edge of the substrate is present below the liquid surface of the solution, wherein the apparatus comprising a reaction vessel for charging a photoresist film removing solution, an ozone feed tube having an outlet for injecting ozone into the photoresist film removing solution, a substrate cassette for disposing and fixing the substrate to contact with a liquid surface of the photoresist film removing solution, a cassette carrier unit for moving the substrate cassette and a processing tank for recovering and processing ozone and/or the photoresist film removing solution. According to the apparatus of the present invention, ozone and the photoresist film removing solution can be simultaneously or separately supplied into the reaction vessel.
In the apparatus of the present invention, the relative position between the surface of the substrate and the liquid surface of the solution may be optionally changed within the range from a position where a bottom edge of the substrate is present above the liquid surface of the solution and another position where a top edge of the substrate is present below the liquid surface of the solution, by continuously or intermittently moving the cassette carrier unit, or by continuously or intermittently controlling the supplement of the photoresist film removing solution into the reaction vessel and the discharge thereof from the reaction vessel.
In the apparatus of the present invention, in case of the supply and discharge of the photoresist film removing solution supply, the reaction vessel may have an automatically operated valve for changing a level of the liquid surface of the photoresist film removing solution.
The apparatus of the present invention further comprises an ultrasound generator. In this case, the removing solution used in the apparatus is preferably supplied in a mixed phase containing ozone, wherein the solution is free from bubbles.
The present invention also provided an apparatus for removing a photoresist film, comprising a substrate cassette for fixing a substrate having a photoresist film on a surface of the substrate, an ozone feed tube, a liquid feed tube for supplying the photoresist film removing solution and a processing tank for recovering and processing ozone and/or the photoresist film removing solution. The photoresist film removing solution supplied through the liquid feed tube may be in a form of liquid or mist, while ozone and the photoresist film removing solution may be continuously or intermittently supplied. The reaction vessel has a means for reusing or discharging the photoresist film removing solution and/or ozone.